Referring to FIG. 1, a conventional reluctance motor 1 includes a stator 11 having eight projecting poles (A, A′, B, B′, C, C′, D, D′), a rotor 12 that is disposed within the stator 11 and that has six salient poles (a, a′, b, b′, c, c′), and four phase windings that are respectively wound around radially opposite pairs of the projecting poles (A-A′, B-B′, C-C′, D-D′) of the stator 11 (hereinafter, phase windings (A″, B″, C″, D″) are used). Usually, the four phase windings (A″, B″, C″, D″) are sequentially switched to a magnetizing state to cause rotation of the rotor 12. For example, the phase winding (A″) may first be switched to the magnetizing state, so that the projecting poles (A, A′) generates magnetic force to attract the salient poles (a, a′) to move toward the projecting poles (A, A′), as shown in FIG. 1. Then, the phase winding (B″) is switched to the magnetizing state, so that the projecting poles (B, B′) generates magnetic force to attract the salient poles (a, a′) to move toward the projecting poles (B, B′). Similarly, the phase windings (C″, D″) are sequentially switched to the magnetizing state, so as to drive clockwise rotation of the rotor 12. In contrast, when the phase windings (A″, B″, C″, D″) are switched to the magnetizing state in a sequence of (D″), (C″), (B″), and (A″), the rotation of the rotor 12 may be driven in a counterclockwise direction.
The conventional reluctance motor 1 operates by magnetic attraction between the projecting poles (A, A′, B, B′, C, C′, D, D′) of the stator 11 and the salient poles (a, a′, b, b′, c, c′) of the rotor 12. However, due to spatial limitation, a number of turns of the phase winding on each projecting pole may be limited (usually less than 100 turns), thereby leading to small reluctance, and requiring a relatively large current to generate sufficient magnetic attraction for driving rotation of the rotor 12. Accordingly, the conventional reluctance motor 1 may not be effectively power-saving.
Referring to FIG. 2, since magnetic power generated by a conventional motor device using the conventional reluctance motor 1 is controlled by current (constant voltage) and since the windings of the reluctance motor are characterized as inductors, counter-electromotive force (Anti-emf), which is denoted using a dashed line in FIG. 2, may be generated during demagnetization of the windings, thereby producing heat that may lead to high temperature of the motor device.
Referring to FIG. 3, since magnetic power generated by a conventional electromagnet is controlled by voltage (constant current) and the winding of the reluctance motor is characterized as an inductor, eddy current, which is denoted using a dashed line in FIG. 3, may be generated during demagnetization of the winding, thereby producing heat.